Systems for harvesting energy from renewable resources have long been pursued in the arts. One of the problems associated with engineering energy harvesting systems is the challenge of making maximum use of energy sources which may be intermittent in availability and/or intensity. Unlike traditional power plants, alternative energy sources tend to have variable outputs. Solar power, for example, typically relies on solar cells, or photovoltaic (PV) cells, used to power electronic systems by charging storage elements such as batteries or capacitors, which then may be used to supply an electrical load. The sun does not always shine on the solar cells with equal intensity however, and such systems are required to operate at power levels that may vary depending on weather conditions, temperature, time of day, shadows from obstructions, and even momentary shadows, causing solar cell power output to fluctuate. Similar problems with output variability are experienced with other power sources such as wind, piezoelectric, regenerative braking, hydro power, wave power, and so forth. It is common for energy harvesting systems to be designed to operate under the theoretical assumption that the energy source is capable of delivering at its maximum output level more-or-less all of the time. This theoretical assumption is rarely matched in practice. Ordinarily, systems are design to be robust enough for anticipated peak loads, but this is done at the expense of efficiency during operation at lower intensity levels.
Switch mode power supplies (SMPS) are commonly used in efforts to efficiently harvest intermittent and/or variable energy source output power for delivery to storage element(s) and/or load(s). The efficiency of the SMPS generally is fairly high, so much so that the power output of the SMPS is often almost equal to the power input to the SMPS. Careful planning and device characterization are often used to attempt to design a system capable of harvesting at the theoretical maximum power level. In a PV system, for example, the maximum power output of a solar cell peaks at a load point specific to the particular solar cell. This maximum power output point varies across different individual solar cells, solar cell arrays, systems in which the solar cells are used, and with the operating environment of system and solar cell. The maximum energy harvesting capability of the electronic system therefore depends on the solar cell characteristics and the characteristics of the load applied to the solar cell. One example of a typical application is an electronic system to harvest energy from a solar cell array in order to charge a battery. Battery charging systems commonly have multiple modes, which include fast charging, charging at full capacity (also called 1C charging), and trickle charging. A typical SMPS regulates output voltage and operates under the theoretical assumption that the power input is capable of delivering the maximum load requirements of the output. In practice, the output impedance of a PV cell is high, so as duty cycle changes, input voltage also changes, which changes the output power of the PV cell. Thus, there is a problem with efficiently exploiting the energy harvesting potential of PV systems and other low and/or variable intensity power sources.
In carrying out the principles of the present invention, in accordance with preferred embodiments, the invention provides advances in the arts with novel apparatus directed to harvesting energy under conditions of both low and high input power. In preferred embodiments, the apparatus includes systems and circuits configured to operate at low power levels and at power levels several orders of magnitude higher. Such systems are designed for harvesting and preferably storing energy available in an operating environment in which power input may vary by several orders of magnitude.
According to aspects of the invention, examples of preferred embodiments include systems for harvesting energy from variable output energy harvesting apparatus suitable for providing energy input to a switched mode power supply. A control loop includes logic for dynamically adjusting energy harvesting apparatus power input to the switched mode power supply, ultimately regulating the system output power signal produced by the switched mode power supply.
According to aspects of the invention, examples of the preferred embodiments include systems for harvesting energy using solar cells.
According to aspects of the invention, examples of preferred embodiments of systems for harvesting energy from variable sources include a boost configuration.
According to aspects of the invention, examples of preferred embodiments of systems for harvesting energy from variable sources include a buck configuration.
According to aspects of the invention, examples of preferred embodiments of systems for harvesting energy from variable sources include a buck-boost configuration.
The invention has advantages including but not limited to one or more of, improved energy harvesting efficiency, improved operating ranges for charging systems, and reduced costs. These and other potential advantageous, features, and benefits of the present invention can be understood by one skilled in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings.
References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as right, left, back, top, bottom, upper, side, et cetera, refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating principles and features as well as advantages of the invention.